Mallia and her daughter Hasana, in Yama, Niger, two of the millions of people whose welfare rests on the decisions made this weekend in Washington. Photograph: Dan Chung

The hopes of 15 million anti-poverty campaigners around the world were pinned last week on the United Nations summit in New York, where international leaders assembled to review progress towards the goals of halving poverty, cutting child deaths and providing universal education by 2015. Yet for all the high profile politicking, the result was deeply disappointing.

Although the summit largely repeated the pledges on aid and debt from July's G8 meeting in Gleneagles, it failed to move things forward, and on trade it backtracked on the promises made in Tony Blair's action plan for Africa. Kofi Annan was barely able to contain his frustration, and spoke of "spoilers" - as close to a tongue-lashing as the UN secretary general gets.

This weekend, much of the summit's unfinished business will resurface, this time at the annual meetings of the World Bank and International Monetary Fund in Washington, DC. The setting is discreet and technocratic, and the meetings rarely make it beyond the economics pages. But there should be no mistaking the significance of what's at stake in Washington. Finance ministers must reach agreement on two issues that have huge implications for the 100 million children who are out of school, and the 850 million people who every night go to bed hungry.

First, the G7 finance ministers' deal agreed earlier this year, to cancel 100% of the debts owed by 18 of the world's poorest countries to the World Bank, IMF and African Development Bank, hangs in the balance. This deal was perhaps the most tangible achievement of the UK government's 2005 poverty agenda, and offered up to $1bn a year in extra money - funds that are urgently needed for primary schools, treatment for HIV and Aids, and clean water.

But now some governments are arguing that countries should jump through extra hoops to get their debts written off. Others are saying that debt repayments, rather than the actual stock of the debt, should be cancelled, which allows creditors to suspend cancellation at will. Meanwhile the IMF and World Bank say that the extra money isn't there, raising the concern that the scheme will be paid for in aid forgone by poor countries that are not indebted - in effect, robbing Peter to pay Paul.

Second, discussions on a review of the conditions tied to World Bank loans have been shelved at the last minute. This is despite the commitment made last year to report back to the annual meetings on the most controversial aspect of the World Bank's work: the requirement that countries open their markets and privatise and deregulate in exchange for aid. These conditions are often to blame for the slow progress on debt relief, because countries must establish a "track record" with the IMF and World Bank before the debts get written off.

In Washington, finance ministers must fully seal the deal on debt with the extra money that's needed, and look to extend it to the dozens of other poor and indebted countries currently outside the scheme. And they must urgently review the use of aid and debt relief conditions by the World Bank and IMF to press risky and unproven policies on some of the world's most vulnerable economies. Backsliding on either of these issues would be a betrayal of the campaigners who came onto the streets of London, Edinburgh and other capitals in the days before the G8 summit. The cost of inaction would be carried by the 1 billion people around the world living today in extreme poverty. This weekend, after the empty grandstanding in New York, world leaders must show they can do better.